1. Field of the Invention
The present invention relates to a technique for determining ambient air temperature outside a passenger compartment of a vehicle, and more specifically to a technique for determining ambient air temperature in the presence of undesired heat load adjacent to the sensor.
2. Background Art
Outside ambient temperature (OAT) sensors are used in vehicles to measure the temperature of ambient air near the OAT sensor. Such OAT sensors are commonly used for climate control as well as for other vehicle functions. For example, OAT sensor readings may be used as an input to a vehicle climate control system for controlling the temperature within the passenger cabin of the vehicle.
However, OAT sensors—when positioned near heat-radiating vehicle components, such as a radiator or an engine block—can produce inaccurate temperature readings when the vehicle is shut off and air is not flowing past the OAT sensor. The worst case for this situation occurs in the summer months when the engine does not cool down as quickly as during other seasons. As a result, when the vehicle is turned off and then back on within a few hours, the sensor produces higher temperature values than the actual ambient temperature.
Previous methods for overcoming erroneous OAT temperature readings have relied on measuring the engine coolant temperature upon vehicle start-up to determine coolant temperature deviation from an expected value with respect to time. The problem with this technique is that vehicles dissipate heat at different rates depending on the vehicle's parking location and parking time duration, among other factors. Hence, for such a vehicle that is turned off and on within a short period of time, the outside ambient temperature reading could conceivably display a much higher temperature than actual. During warmer times of the year, this could cause the air conditioning of an automatic climate control system to erroneously turn on at the highest setting, causing customer dissatisfaction.
Accordingly, what is needed is an improved outside ambient temperature start-up method to reliably calculate an outside ambient temperature value in the presence of undesirable heating effects on the OAT sensor.